Adsorption and reactions of propenoic acid and 2-fluoropropanoic acid on Cu(100) and O/Cu(100)

X-ray photoelectron spectroscopy, reflection-absorption infrared spectroscopy, and temperature-programmed reaction/desorption have been employed to investigate the adsorption and reaction pathways of CH ₂ =CHCOOH and CH ₃ CHFCOOH on Cu(100) and oxygen-precovered Cu(100) [O/Cu(100)]. In the case of CH ₂ =CHCOOH on O/Cu(100), CH ₂ =CHCOO is the surface intermediate detected between 110 K and 400 K. CH ₂ =CHCOO is adsorbed vertically and can change adsorption sites at a higher temperature. The propenoate (acrylate) decomposes at higher temperatures (>500 K), with formation of >C=C=O (ketenylidene) surface species and gaseous products. On Cu(100), CH ₂ =CHCOOH is adsorbed in dimer form and can dissociate to generate CH ₂ =CHCOO and CH ₃ CHCOO intermediates on the surface. The CH ₃ CHCOO continuously recombines with the H from deprotonation of CH ₂ =CHCOOH, resulting in the formation CH ₃ CH ₂ COO. The co-existing CH ₂ =CHCOO and CH ₃ CH ₂ COO further decompose at ∼550 K to evolve reaction products, but without >C=C=O being detected. On O/Cu(100), CH ₃ CHFCOOH readily deprotonates to form CH ₃ CHFCOO at 120 K. This intermediate reacts on the surface at ∼460 K to evolve gaseous products, also producing CH ₂ =CHCOO. In the case of Cu(100), deprotonation of CH ₃ CHFCOOH occurs at ∼250 K, forming CH ₃ CHFCOO. Without oxygen on the surface, this intermediate decomposes into HF and CH ₂ =CHCOO at ∼455 K.